Adrenal chromaffin cells contain high affinity saturable benzodiazepine and GABA binding sites. The pharmacological specificity and the interaction between these two binding sites is similar to that reported in brain. However, the benzodiazepine binding sites of adrenal medulla cells have a low affinity (100 nM) for 3-carboxylate esters of beta-carbolines. Adrenal chromaffin cells also contain Gamma-aminobutyric acid, glutamic acid decarboxylase, GABA aminotransferase, and GABA receptors appear to modulate the acetylcholine-induced release of catecholamines and enkephalin-like peptides in opposite directions.